ni845x_spi: Make ni845x_spi_init() static

We have moved the programmer definitions into the respective source
files long ago. We missed to make this init function static, so GCC
and Clang warn about it now.

Change-Id: I9a99926e63eacbcccd938c8c3d828aa9a18acc32
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/408
diff --git a/ni845x_spi.c b/ni845x_spi.c
index c1dd59c..a475598 100644
--- a/ni845x_spi.c
+++ b/ni845x_spi.c
@@ -390,7 +390,7 @@
 		ni845x_report_error("ni845xCloseFindDeviceHandle", tmp);
 }
 
-int ni845x_spi_init(struct flashprog_programmer *const prog)
+static int ni845x_spi_init(struct flashprog_programmer *const prog)
 {
 	char *speed_str = NULL;
 	char *CS_str = NULL;