MIPS: initialize board_init_f() argument to zero.

Argument boot_flags of board_init_f() should be set to 0 as
$a0 may be utilized in lowlevel_init() or mips_cache_reset()
or previous stage boot-loader.

Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

arch/mips/cpu/start.S

@@ -185,7 +185,7 @@ reset:
 	PTR_ADDU t0, k0, GD_MALLOC_BASE	# gd->malloc_base offset
 	sw	sp, 0(t0)
 #endif
-
+	move	a0, zero		# a0 <-- boot_flags = 0
 	PTR_LA	t9, board_init_f
 	jr	t9
 	 move	ra, zero