qcom: pd-mapper: Null terminate firmware_value string

cherry-picked from upstream device/linaro/dragonboard project.

Null terminate firmware_value string to prevent
strlen() read past the end of buffer.

Otherwise pd-mapper will crash:
  console:/ # pd-mapper
  FORTIFY: strlen: detected read past end of buffer
  Aborted
  134|console:/ #

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: Id0b9e1dda2bae12e3a36f1ce40376d1161878894
diff --git a/qcom/pd-mapper/pd-mapper.c b/qcom/pd-mapper/pd-mapper.c
index f26710d..c7db57f 100644
--- a/qcom/pd-mapper/pd-mapper.c
+++ b/qcom/pd-mapper/pd-mapper.c
@@ -241,6 +241,8 @@
 			continue;
 		}
 
+		firmware_value[n] = '\0';
+
 		if (strlen(FIRMWARE_BASE) + strlen(firmware_value) + 1 > sizeof(path))
 			continue;