armv8m: Don't allow signed integer overflow

To avoid undefined behavior, replace the signed "times" counter with an unsigned one. We don't need to track negative times anyway.

./core/vmpu/src/mpu_armv8m/vmpu_armv8m_unpriv_access.c: In function 'vmpu_unpriv_access':
./core/vmpu/src/mpu_armv8m/vmpu_armv8m_unpriv_access.c:126:1: error: assuming signed overflow does not occur when changing X +- C1 cmp C2 to X cmp C2 -+ C1 [-Werror=strict-overflow]
 }
  ^
  ./core/vmpu/src/mpu_armv8m/vmpu_armv8m_unpriv_access.c:94:10: error: assuming signed overflow does not occur when changing X +- C1 cmp C2 to X cmp C2 -+ C1 [-Werror=strict-overflow]
   uint32_t vmpu_unpriv_access(uint32_t addr, uint32_t size, uint32_t data)

Author: Patater

core/vmpu/src/mpu_armv8m/vmpu_armv8m_unpriv_access.c

@@ -93,7 +93,7 @@ extern int vmpu_fault_recovery_mpu(uint32_t pc, uint32_t sp, uint32_t fault_addr
 
 uint32_t vmpu_unpriv_access(uint32_t addr, uint32_t size, uint32_t data)
 {
-    int tries = 0;
+    unsigned int tries = 0;
     while(1) {
         if ((vmpu_unpriv_test_range(addr, UVISOR_UNPRIV_ACCESS_SIZE(size)) & (TT_RESP_NSRW_Msk | TT_RESP_SRVALID_Msk)) == (TT_RESP_NSRW_Msk | TT_RESP_SRVALID_Msk)) {
             switch(size) {