cgexec: Fix clang warnings

cgexec: Fix clang warnings

Fix the following clang warnings by shrinking the scan size from 4096 to
4095 to allow room for the null terminating character.

	cgexec.c:294:47: warning: 'sscanf' may overflow; destination buffer in
	argument 4 has size 4096, but the corresponding specifier may require
	size 4097 [-Wfortify-source]
	  294 |                         ret = sscanf(buffer, "%d::%4096s\n",
	&idx, cgrp_name);
	      |
	^
	cgexec.c:296:63: warning: 'sscanf' may overflow; destination buffer in
	argument 5 has size 4096, but the corresponding specifier may require
	size 4097 [-Wfortify-source]
	  296 |                         ret = sscanf(buffer,
	"%d:%[^:]:%4096s\n", &idx, ctrl_name, cgrp_name);
	      |
	^
	cgexec.c:423:40: warning: 'sscanf' may overflow; destination buffer in
	argument 3 has size 4096, but the corresponding specifier may require
	size 4097 [-Wfortify-source]
	  423 |                 ret = sscanf(buffer, "%*s %4096s\n", cgrp_path);
	      |                                                      ^

Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>