Bug 1841917 - Fix "variable does not need to be mutable" warnings. r=keeler

Differential Revision: https://phabricator.services.mozilla.com/D182848

security/manager/ssl/ipcclientcerts/src/lib.rs

@@ -455,7 +455,7 @@ extern "C" fn C_GetAttributeValue(
         return CKR_DEVICE_ERROR;
     }
     for i in 0..ulCount as usize {
-        let mut attr = unsafe { &mut *pTemplate.offset(i as isize) };
+        let attr = unsafe { &mut *pTemplate.offset(i as isize) };
         // NB: the safety of this array access depends on the length check above
         if let Some(attr_value) = &values[i] {
             if attr.pValue.is_null() {

security/manager/ssl/osclientcerts/src/lib.rs

@@ -534,7 +534,7 @@ extern "C" fn C_GetAttributeValue(
         return CKR_DEVICE_ERROR;
     }
     for (i, value) in values.iter().enumerate().take(ulCount as usize) {
-        let mut attr = unsafe { &mut *pTemplate.add(i) };
+        let attr = unsafe { &mut *pTemplate.add(i) };
         if let Some(attr_value) = value {
             if attr.pValue.is_null() {
                 attr.ulValueLen = attr_value.len() as CK_ULONG;