powerpc: udbg_memcons: mark functions static

ppc64_book3e_allmodconfig has one more driver that triggeres a
few missing-prototypes warnings:

arch/powerpc/sysdev/udbg_memcons.c:44:6: error: no previous prototype for 'memcons_putc' [-Werror=missing-prototypes]
arch/powerpc/sysdev/udbg_memcons.c:57:5: error: no previous prototype for 'memcons_getc_poll' [-Werror=missing-prototypes]
arch/powerpc/sysdev/udbg_memcons.c:80:5: error: no previous prototype for 'memcons_getc' [-Werror=missing-prototypes]

Mark all these function static as there are no other users.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240123125148.2004648-1-arnd@kernel.org

arch/powerpc/sysdev/udbg_memcons.c

@@ -41,7 +41,7 @@ struct memcons memcons = {
 	.input_end = &memcons_input[CONFIG_PPC_MEMCONS_INPUT_SIZE],
 };
 
-void memcons_putc(char c)
+static void memcons_putc(char c)
 {
 	char *new_output_pos;
 
@@ -54,7 +54,7 @@ void memcons_putc(char c)
 	memcons.output_pos = new_output_pos;
 }
 
-int memcons_getc_poll(void)
+static int memcons_getc_poll(void)
 {
 	char c;
 	char *new_input_pos;
@@ -77,7 +77,7 @@ int memcons_getc_poll(void)
 	return -1;
 }
 
-int memcons_getc(void)
+static int memcons_getc(void)
 {
 	int c;