riscv: Suppress invalid coverity errors

Coverity is detecting 'sp' as a variable which has not been initialized.
This is obviously not correct, so this patch *TRIES* to mark it as false

I'm not positive that this will work because the annotation needs to go
on the line above the error, but this error is inside of a # define.

Does the whole #define count as one line?  Can it go on the line
above the #define in the .h file?  Does it have to precede every line
where the #define is used?  The documentation doesn't make this clear.

Should suppress coverity issues: 1368525 & 1368527
uninit_use: Using uninitialized value sp.

Change-Id: Ibae5e206c4ff47991ea8a11b6b59972b24b71796
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/18247
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

src/arch/riscv/include/mcall.h

@@ -70,6 +70,7 @@ typedef struct {
 } hls_t;
 
 #define MACHINE_STACK_TOP() ({ \
+  /* coverity[uninit_use] : FALSE */ \
   register uintptr_t sp asm ("sp"); \
   (void*)((sp + RISCV_PGSIZE) & -RISCV_PGSIZE); })