arm: mxs: Scrub useless ifdef

As a result of 0defddc851edfc34bcf3c3379fe74b11dc01a493 , which did
a consolidation of the prompt string, this ifdef became empty. Remove
it.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@ti.com>
Cc: Stefano Babic <sbabic@denx.de>

include/configs/mxs.h

@@ -94,8 +94,6 @@
 
 /* U-Boot general configuration */
 #define CONFIG_SYS_LONGHELP
-#ifndef CONFIG_SYS_PROMPT
-#endif
 #define CONFIG_SYS_CBSIZE	1024		/* Console I/O buffer size */
 #define CONFIG_SYS_PBSIZE	\
 	(CONFIG_SYS_CBSIZE + sizeof(CONFIG_SYS_PROMPT) + 16)