powerpc/64: Drop unnecessary 'rc' variable

Simplify the code to enhance readability and maintain a consistent
coding style.

Signed-off-by: Xichao Zhao <zhao.xichao@vivo.com>
Acked-by: Gautam Menghani <gautam@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250801035908.370463-1-zhao.xichao@vivo.com

Author: Xichao Zhao

arch/powerpc/kernel/setup_64.c

@@ -141,10 +141,7 @@ void __init check_smt_enabled(void)
 			smt_enabled_at_boot = 0;
 		else {
 			int smt;
-			int rc;
-
-			rc = kstrtoint(smt_enabled_cmdline, 10, &smt);
-			if (!rc)
+			if (!kstrtoint(smt_enabled_cmdline, 10, &smt))
 				smt_enabled_at_boot =
 					min(threads_per_core, smt);
 		}