Fix checkpatch issue - ERROR:ASSIGN_IN_IF

Assignment in if condition should be avoided. The source code is
restructured to have the assignment outside the if condition.

Signed-off-by: Yonattan Louise <yonattan.a.louise.mendoza@intel.com>
Change-Id: I9e3e1d069657d3ce9f54e1f4b4b74163c724a733
Signed-off-by: Anas Nashif <anas.nashif@intel.com>

lib/libc/minimal/source/stdout/prf.c

@@ -622,7 +622,8 @@ int _prf(int (*func)(), void *dest, char *format, va_list vargs)
 				width = MAXFLD;
 
 			if (c == '.') {
-				if ((c = *format++) == '*') {
+				c = *format++;
+				if (c == '*') {
 					precision = (int32_t)
 					va_arg(vargs, int32_t);
 				} else