Fix device map check for paged attn

[EricLBuehler]

Device mapping is incompatible with PagedAttention because the KV cache needs to all be on 1 GPU.

[github-actions]

Code Metrics Report

  ===============================================================================
 Language            Files        Lines         Code     Comments       Blanks
===============================================================================
 C Header                2           35           28            0            7
 Dockerfile              1           34           25            0            9
 Happy                   1          442          369            0           73
 JSON                   11          102          101            0            1
 Python                 43         1816         1550           56          210
 TOML                   19          574          506           11           57
-------------------------------------------------------------------------------
 Jupyter Notebooks       3            0            0            0            0
 |- Markdown             2           77           32           31           14
 |- Python               2          196          169            1           26
 (Total)                            273          201           32           40
-------------------------------------------------------------------------------
 Markdown               25         1841            0         1384          457
 |- BASH                 5          101           98            0            3
 |- JSON                 1           12           12            0            0
 |- Python               5           92           82            0           10
 |- Rust                 6          408          365           19           24
 |- TOML                 2           75           63            0           12
 (Total)                           2529          620         1403          506
-------------------------------------------------------------------------------
 Rust                  173        55372        50266          988         4118
 |- Markdown            92          849           13          786           50
 (Total)                          56221        50279         1774         4168
===============================================================================
 Total                 279        60216        52845         2439         4932
===============================================================================