m68k: coldfire: make mcf_maskimr() static

When building with W=1:

      CC      arch/m68k/coldfire/intc.o
    arch/m68k/coldfire/intc.c:83:6: warning: no previous prototype for ‘mcf_maskimr’ [-Wmissing-prototypes]
     void mcf_maskimr(unsigned int mask)
          ^~~~~~~~~~~

The mcf_maskimr() function is only used within this file, make it static
to reduce name space pollution and fix warning.
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>

arch/m68k/coldfire/intc.c

@@ -56,7 +56,7 @@ void mcf_clrimr(int index)
 	__raw_writew(imr & ~(0x1 << index), MCFSIM_IMR);
 }
 
-void mcf_maskimr(unsigned int mask)
+static void mcf_maskimr(unsigned int mask)
 {
 	u16 imr;
 	imr = __raw_readw(MCFSIM_IMR);
@@ -80,7 +80,7 @@ void mcf_clrimr(int index)
 	__raw_writel(imr & ~(0x1 << index), MCFSIM_IMR);
 }
 
-void mcf_maskimr(unsigned int mask)
+static void mcf_maskimr(unsigned int mask)
 {
 	u32 imr;
 	imr = __raw_readl(MCFSIM_IMR);