MIPS: Make declaration for function memory_region_available static

Fix non-fatal warning during compilation using W=1:

arch/mips/kernel/setup.c:158:13: warning: no previous prototype for ‘memory_region_available’ [-Wmissing-prototypes]
 bool __init memory_region_available(phys_addr_t start, phys_addr_t size)
             ^~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Mathieu Malaterre <malat@debian.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18175/
[jhogan@kernel.org: tweak whitespace]
Signed-off-by: James Hogan <jhogan@kernel.org>

arch/mips/kernel/setup.c

@@ -155,7 +155,8 @@ void __init detect_memory_region(phys_addr_t start, phys_addr_t sz_min, phys_add
 	add_memory_region(start, size, BOOT_MEM_RAM);
 }
 
-bool __init memory_region_available(phys_addr_t start, phys_addr_t size)
+static bool __init __maybe_unused memory_region_available(phys_addr_t start,
+							  phys_addr_t size)
 {
 	int i;
 	bool in_ram = false, free = true;