modif: Change errExit msg format to match assert

Make it more similar to the assert() message format for consistency.
Example:

Before:

    firejail: main.c:100: main: Assertion `1 == 2' failed.
    Error src/firecfg/main.c:100 main(): malloc: Cannot allocate memory

After:

    firejail: main.c:100: main: Assertion `1 == 2' failed.
    Error src/firecfg/main.c:100: main: malloc: Cannot allocate memory

This amends commit b963fe4 ("Improve errExit error messages",
2023-06-16) / PR netblue30#5871.

src/include/common.h

@@ -41,7 +41,7 @@
 
 #define errExit(msg) do { \
 	char msgout[500]; \
-	snprintf(msgout, 500, "Error %s/%s:%d %s(): %s", \
+	snprintf(msgout, 500, "Error %s/%s:%d: %s: %s", \
 	         MOD_DIR, __FILE__, __LINE__, __func__, msg); \
 	perror(msgout); \
 	exit(1); \