powerpc/85xx: Make c293_pcie_pic_init() static

To fix the W=1 warning:
  linux/arch/powerpc/platforms/85xx/c293pcie.c:22:13: error: no previous prototype for ‘c293_pcie_pic_init’
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211124093254.1054750-3-mpe@ellerman.id.au

arch/powerpc/platforms/85xx/c293pcie.c

@@ -19,7 +19,7 @@
 
 #include "mpc85xx.h"
 
-void __init c293_pcie_pic_init(void)
+static void __init c293_pcie_pic_init(void)
 {
 	struct mpic *mpic = mpic_alloc(NULL, 0, MPIC_BIG_ENDIAN |
 	  MPIC_SINGLE_DEST_CPU, 0, 256, " OpenPIC  ");