Fix .asciiz string encoding for ecall5 instruction

[Maryam-Gamal]

Bug Description:

The bug is in the .asciiz directive. When processing .asciiz strings, the original code incorrectly packs characters into 16-bit words, which causes problems when these strings are used with the ecall 5 instruction.

---

Example:

.text 

    .org    0 

main: 

    lui     a0, %hi(0x100) 

    ecall   5               # service 5 to print a string 

exit: 

    ecall   3 

    .data 

    .org    0x100 

 str:    

    .asciiz "hello world" 

---

Expected Behavior:

Each character in the .asciiz string should be stored as a separate byte .

Actual Behavior:

As shown in the screenshot of the bin file, characters are incorrectly packed, causing incorrect string representation.