MIPS: pmcs-msp71xx: Add missing MAX_PROM_MEM definition

Commit b3c948e2 ("MIPS: msp: Record prom memory") introduced use of
a MAX_PROM_MEM value but didn't define it. A bounds check in
prom_meminit() suggests its value was supposed to be 5, so define it as
such & adjust the bounds check to use the macro rather than a magic
number.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: b3c948e2 ("MIPS: msp: Record prom memory")
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-mips@vger.kernel.org

arch/mips/pmcs-msp71xx/msp_prom.c

@@ -61,6 +61,7 @@ int init_debug = 1;
 /* memory blocks */
 struct prom_pmemblock mdesc[PROM_MAX_PMEMBLOCKS];
 
+#define MAX_PROM_MEM 5
 static phys_addr_t prom_mem_base[MAX_PROM_MEM] __initdata;
 static phys_addr_t prom_mem_size[MAX_PROM_MEM] __initdata;
 static unsigned int nr_prom_mem __initdata;
@@ -358,7 +359,7 @@ void __init prom_meminit(void)
 		p++;
 
 		if (type == BOOT_MEM_ROM_DATA) {
-			if (nr_prom_mem >= 5) {
+			if (nr_prom_mem >= MAX_PROM_MEM) {
 				pr_err("Too many ROM DATA regions");
 				continue;
 			}