Remove always-false null pointer check in sha3.c that Coverity complains about

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/library/sha3.c b/library/sha3.c
index dca5790..4c1a1a9 100644
--- a/library/sha3.c
+++ b/library/sha3.c
@@ -200,7 +200,7 @@
         }
     }
 
-    if (p == NULL || p->id == MBEDTLS_SHA3_NONE) {
+    if (p->id == MBEDTLS_SHA3_NONE) {
         return MBEDTLS_ERR_SHA3_BAD_INPUT_DATA;
     }